To Bond or Not to Bond?

Q.As a building inspector, I
understand Article 250 of the most recent National
Electrical Code (2005 NEC) to mean that any potential
grounding electrodes available to each electrical
service must be bonded together into that service's
grounding electrode system. But the code also says that
an underground gas piping system may not be used as a
grounding electrode. Some of my colleagues believe this
means that gas pipes should not be bonded to the water
pipes, while I believe that they should be. Who is
right?

A.George Flach, former
chief electrical inspector for New Orleans,
responds: Gas pipes often supply equipment and
appliances that are also powered electrically
— such as gas-electric central heating
furnaces and gas heaters with pumps used for
warming water in swimming pools, or gas clothes
dryers and gas ranges with illuminated ovens and
spark igniters — and they may become
energized by the branch circuits that power these
units.

To reduce that risk, Section 250.104(B) of the
2005 NEC requires that all gas pipe be bonded.
However, the NEC also recognizes the equipment
grounding conductor of each branch circuit as a
bonding means for the gas piping, and requires no
additional bonding or grounding.

Still, there's no reason gas pipes can't be
bonded to the water pipes. Gas utility companies
usually equip their underground metal gas
distribution systems with cathodic protection,
typically with an isolation coupling or union at
each customer's gas-pipe connection. Grounding and
bonding of the customer-owned gas piping system
won't interfere with this cathodic protection. And
as the note following NEC 250.104(B) emphasizes,
it's always a good idea to bond all metal piping
and metal air ducts.

There are no changes to 250.104(B) in the
pending edition of the 2008 NEC.